stream incision, tectonics, uplift, and evolution of...
TRANSCRIPT
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Stream Incision, Tectonics, Uplift, and Evolution of Topography of the Sierra Nevada, California
John Wakabayashi and Thomas L. Sawyer
The Journal of Geology, 2001
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background
• Sierra Nevada microplate
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background
• Sierra Nevada microplate
• Cenozoic Volcanics
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background
• Sierra Nevada microplate
• Cenozoic Volcanics
– distribution?
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background
• Sierra Nevada microplate
• Cenozoic Volcanics
• important stratigraphy
– Crystallization ages of plutons (110-85Ma)
– Eocene (57-34Ma) auriferous gravels/Ione Formation
– 34-20Ma rhyolites
– 14-4Ma andesites & volcaniclastics: Mehrten Formation
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• Slip rates
– ‘d’ = dip slip fault
– ‘s’ = dextral strike slip fault
• Frontal fault system dextral “Walker Lane Belt”
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• Frontal fault system
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intro II
• Slip rates
– ‘d’ = dip slip fault
– ‘s’ = dextral strike slip fault
• Frontal fault system
• Internal deformation
– “rigid block model”?
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stream incision
• Terminology:
– “total incision” vs “basement incision”
• How are incision rates determined?
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stream incision
#s represent: Total incision [m]
(basement incision [m])
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stream incision
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paleorelief
(i.e. relief predating Cenozoic deposits)
• how is this calculated?
• Differences between north/central and southern Sierra?
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Late Cenozoic action on Frontal Fault System
• Beheaded drainages and volcanic rocks provide timing/magnitude of vertical displacement on front
• westward encroachment of WLB
Internal deformation of ‘rigid’ Sierra block
• Rigid model appropriate?
• Why is it important?
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Uplift • What are we talking about???
– Surface uplift
– Exhumation
– Rock uplift
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Uplift • What are we talking about???
– Surface uplift
– Exhumation
– Rock uplift
• Geometric relationships:
– What are two alternative uplift hypotheses explained by tilted strata?
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Uplift history 100-60Ma: early exhumation, erosion, and associated surface uplift •Thermochron •Sed accum (Great Valley Group) •Erosion Rates
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Uplift history Eocene-Miocene: negligible uplift •Less tilt •Incision reduced •Sed Accumulation Rates in Central Valley
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Uplift history Late Cenozoic uplift •Tilting •Increased incision/relief •Increased sedimentation
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3 methods of estimating rock uplift
from tilted Cenozoic strata
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How did they construct this
paleotopography?
North/Central vs. South
What do you think about the pre-
Cenozoic paleoelevation/paleorelief
implications of this map?
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All tectonic uplift?
What about:
• Isostatic response to
Sierra erosion/Central
Valley deposition
• Climatic
considerations?
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